Not applicable.
Not applicable.
Not applicable.
The object of the present invention is a set of burs for preparing a tooth with a view to placing a prosthetic crown.
Before placing a prosthetic crown on a tooth, it is necessary to machine said tooth, so as to remove the material that will be replaced by said prosthetic crown.
Since the size characteristics of the prosthetic crown should preferably be identical to those of the initial tooth, the four faces and the crown portion of said tooth are machined.
The operation is particularly delicate, since it is absolutely necessary to spare the papilla and the gum and to avoid damaging the adjacent teeth that are often very close to the tooth to be treated, whereby one should know that the practitioner has not always a bearing point at his disposal.
Furthermore, in order to achieve a perfect adjustment of the prosthetic crown, it is necessary for the faces to be homothetically machined according to the drawings, whereby one should know that, in the case of an incisor, the vestibular face is convex and the lingual face is concave, that, in the case of the pre-molar and the molar teeth, the faces are convex and that, in addition, the convex faces are so both in the cervical-occiusal direction and in the mesio-distal direction.
Currently, to achieve this aim, the preparation of a tooth starts by making a mesio-distal groove, then the occlusal portion and then the cervical portion are machined using the bottom of said groove as a depth control; while the last operation consists of creating a shoulder at the level of the collar, the fillet of which is preferably at a right angle in front of the gum papilla.
The drills that allow carrying out these operations are e.g. of the kind of those disclosed in FR 2,481,105 and in DE 2,012,268. These drills include, in a known way, one or several active portions and one or several inactive portions that provide the practitioner with a bearing point, without damaging the bearing area.
However, the burs of this kind do not allow the practitioner to prepare a tooth in a fully calm way, because of the requirements to be fulfilled.
Though the active portions of these burs indeed provide for a bearing point for carrying out the machining, they do not allow controlling the machining depth, namely when making the cervical fillet.
From GB 379,200 are known so-called xe2x80x9cBATTxe2x80x9d drills for intra-coronary use that allow, in particular, the ablation of the pulp ceiling, im order to treat the pulp eviction in the best possible way. These burs can have an ovoid or elongated shape and include, each, two portions, an active proximal portion and an inactive distal end. The bur is cylindrical, cylindrical-conical or ovoid and its distal end is semi-spherical in the case of the cylindrical and cylindrical-conical burs and parabolic in the case of the ovoid burs, the inactive portion covering at least the semi-spherical area in the case of the cylindrical and cylindrical-conical burs and a parabolic area of a height substantially equal to or larger than the radius of curvature of the end portion im the case of the ovoid burs.
Because of these features, namely the inactivity of the distal portion, these burs only allow boring out a cavity through a pivotal motion and a sliding about a point of the inactive portion. Because of its relatively large surface, namely with respect to its radius of curvature, the inactive portion is suitable only for machining a pulp ceiling and can in no way allow machining the coronary portion of a tooth.
From FR 2,716,795, there are also known dental burs including at least an inactive portion and an active portion, which are aimed at preparing a tooth with a view to placing a prosthetic crown. These drills, which must allow machining the tooth simultaneously over its full height, do not allow an accurate work and, in particular, do not to control the machining depth, namely when these drills have a flat active distal end.
The present invention is aimed at providing a set of burs for preparing a tooth, with a view to placing a prosthetic crown, that allows coping with the various above-mentioned drawbacks.
The set of burs for preparing a tooth with a view to placing a prosthetic crown, in which said burs are of the kind including an active portion and at least one inactive portion, is characterized mainly in that each of them includes a distal end having the shape of a portion of a sphere that has an inactive portion and an active portion, one of which consists of a spherical cap in an apical position having a small circle with a radius much smaller than its radius of curvature.
According to the invention, the apical spherical cap is inactive.
According to a particular embodiment of the set of burs according to the invention, one bur includes a head having the shape of a sphere or the like.
According to another particular embodiment of the set of burs according to the invention, one bur has the shape of a cylinder, the cylindrical surface of which is inactive and the distal end of which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder.
According to a particular embodiment of the set of burs according to the invention, one bur has the shape of a cylinder, its cylindrical surface being inactive, while its distal end, which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder, has, besides an inactive apical cap, an inactive peripheral area, so that the active portion of said distal end extends over a spherical ring.
According to another particular embodiment of the set of burs according to the invention, one bur has a cylindrical or cylindrical-conical shape the cylindrical or cylindrical-conical surface of which is active, while the distal end is semi-spherical.
According to the invention, the apical spherical cap is active.
According to a particular embodiment of the set of burs according to the invention, one said bur has the shape of a cylinder, its cylindrical surface being inactive, while its distal end, which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder, has an active apical spherical cap bordered by an inactive spherical ring.
According to another particular embodiment of the set of burs according to the invention, one said bur has the shape of a cylinder, its cylindrical surface being inactive, while its distal end, which has the shape of a spherical cap with a radius of curvature larger than that of said cylinder, has an active apical spherical cap bordered by an inactive beveled rim.